Some communication systems transmit data from a transmitter to a receiver over multiple communication channels, using multiple transmit antennas and multiple receive antennas. Multiple-channel transmission is used, for example, in spatial multiplexing schemes that achieve high throughput, in beam-forming schemes that achieve high antenna directivity and in spatial diversity schemes that achieve high resilience against channel fading and multipath. These schemes are often referred to collectively as Multiple-Input Multiple-Output (MIMO) schemes.
MIMO schemes are contemplated, for example, for use in Evolved Universal Terrestrial Radio Access (E-UTRA) systems, also referred to as Long Term Evolution (LTE) systems. The Third Generation Partnership Project (3GPP) E-UTRA standards specify MIMO schemes for use by E-UTRA User Equipment (UE) and base stations (eNodeB). These schemes are described, for example, in 3GPP Technical Specification 36.211, entitled “Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 8),” (3GPP TS 36.211), version 8.6.0, March, 2009, which is incorporated herein by reference. The 3GPP is currently in the process of specifying an extension of the E-UTRA specification, which is referred to as LTE-Advanced (LTE-A).
Multi-User MIMO (MU-MIMO) is a transmission scheme in which a transmitter transmits MIMO signals simultaneously to two or more different receivers, using spatial multiplexing. Several aspects of the potential use of MU-MIMO in LTE-A are discussed, for example, in “CQI Reporting for MU-MIMO,” 3GPP TSG RAN WG1 Meeting #54, Document R1-082874, Jeju, Korea, Aug. 18-22, 2008; in “Some Results on DL-MIMO Enhancements for LTE-A,” 3GPP TSG RAN WG1 Meeting #55, Document R1-090328, Ljubljana, Slovenia, Jan. 12-16, 2009; and in “‘Best Companion’ Reporting for Improved Single-Cell MU-MIMO Pairing, 3GPP TSG RAN WG1 Meeting #56, Document R1-090926, Athens, Greece, Feb. 9-13, 2009, which are incorporated herein by reference.
The description above is presented as a general overview of related art in this field and should not be construed as an admission that any of the information it contains constitutes prior art against the present patent application.